1. Field of the Invention
This invention relates to a method of manufacturing and a manufacturing apparatus for a piezoelectric thin film resonator in which a lower electrode, a piezoelectric film, and an upper electrode are formed in order on a substrate, a piezoelectric thin film resonator manufactured according to this method of manufacturing, and an electronic component constructed so as to include this piezoelectric thin film resonator.
2. Description of the Related Art
As one example of a piezoelectric thin film resonator manufactured according to this kind of method of manufacturing, a piezoelectric thin film element for use as a filter or the like in an electronic appliance, such as a mobile phone, is disclosed by Japanese Laid-Open Patent Publication No. 2001-251159. This piezoelectric thin film element is constructed by forming a lower electrode, a piezoelectric film, and an upper electrode in that order on a silicon substrate. In this case, the silicon substrate is a substrate for a piezoelectric thin film element with a silicon oxide film being formed on an upper surface thereof and a layer of a mask material being formed on a lower surface thereof. Also, a cavity for resonance is formed in the silicon substrate so that during driving, formed in the silicon substrate so that during driving, the lower electrode, the piezoelectric film and the upper electrode can resonate.
When manufacturing this piezoelectric thin film element, first a metal film for forming the lower electrode is formed on the silicon oxide film on the silicon substrate and etching is then carried out to leave parts of the metal film corresponding to the lower electrode and remove unnecessary parts, thereby forming the lower electrode. At this time, as one example, a mask is formed by forming a photoresist layer on the metal film and then exposing and developing the photoresist layer, and then etching is carried out using this mask. Next, the piezoelectric film is formed so as to cover the lower electrode by carrying out sputtering, for example, on the silicon substrate. After this, after the metal film for forming the upper electrode has been formed on the piezoelectric film, etching is carried out to leave parts of the metal film corresponding to the upper electrode and remove unnecessary parts, thereby forming the upper electrode. At this time, in the same way as when the lower electrode is formed, etching is carried out using a mask formed by exposing and developing a photoresist layer, for example. Next, etching is carried out with the mask material formed on the lower surface of the silicon substrate as a mask to form the resonance cavity. After this, by applying an organic resin material so as to cover the piezoelectric film and the upper electrode, an organic resin film is formed, thereby completing the piezoelectric thin film element.
However, by investigating the conventional method of manufacturing a piezoelectric thin film element, the inventors of the present invention discovered the following problem. That is, the conventional method of manufacturing forms the upper electrode by etching a metal film formed on the piezoelectric film. Accordingly, if the upper electrode is formed by wet etching, depending on the combination of the material forming the piezoelectric film and the metal(s) forming the upper electrode, when the etching liquid removes unnecessary parts of the metal film and contacts the surface of the piezoelectric film, the etching liquid for etching the metal film also etches the piezoelectric film. Also, if etching is completed just before the etching liquid starts to etch the piezoelectric film, some parts of the metal film that should be removed will definitely remain on the piezoelectric film. In this case, if the piezoelectric film is etched or parts of the metal film unintentionally remain, the electrical characteristics of the piezoelectric thin film element will not satisfy the desired characteristics for which the piezoelectric thin film element was designed. Accordingly, it is necessary to carry out etching so as to completely remove unnecessary parts of the metal film without etching the piezoelectric film. However, the time required to completely etch the metal film changes every time etching is carried out due to factors such as minute variations in the thickness of the metal film and changes in the temperature of the etching liquid. Accordingly, with the conventional method of manufacturing a piezoelectric thin film element, there is the problem that it is difficult to completely remove unnecessary parts of the metal film without etching the piezoelectric film when forming the upper electrode.